Widely used are methods for blending and finely dispersing a polymer having a low glass transition temperature in a shape of a particle in a resin constituting a matrix, such as a thermoplastic resin, a thermosetting resin, or an elastomer, in order to improve its mechanical properties, such as impact resistance and tensile properties. As examples of the polymer, polyorganosiloxanes, polyalkyl (meth)acrylates (having a low glass transition temperature), polybutadienes, etc. may be mentioned. Blending especially of the polyorganosiloxane to the matrix resin may develop various effects including improvement in low-temperature characteristics or flame retardancy by utilizing the physical characteristics, such as outstanding low-temperature characteristics, and unique reactivity of a polyorganosiloxane component.
However, since such polymers having a low glass transition temperature, especially polyorganosiloxanes, have poor compatibility with generally known resin components, and the polyorganosiloxane cannot fully develop fine dispersion or homogeneity in a shaped article obtained by being blended and kneaded with the matrix resin, there may easily occur problems, such as deterioration of appearance, and decrease in mechanical strength caused by delamination. Therefore, many investigations for overcoming the problems have been made, for example, wherein a resin component having compatibility with the matrix resin is chemically combined with the polyorganosiloxane component to form a block copolymer or a graft copolymer. Especially a graft copolymer having the above mentioned resin component grafted to a polyorganosiloxane component advantageously enables control of dispersion of the polyorganosiloxane component in the matrix resin.
A method is publicly known wherein since the polyorganosiloxane component has poor reactivity with vinyl monomers forming the resin component, a graft copolymer is efficiently formed using a polyorganosiloxane modified with a unit of so-called graft-linking agent having radical polymerization reactivity. However, left behind is a problem that in generally known graft copolymers, not all of the resin components are necessarily grafted to the polyorganosiloxane component, and a part of them exists in a separated state, and in case of a large percentage of the resin component in the separated state, for example, the polyorganosiloxane component agglomerates in the shaped article to deteriorate dispersion, failing to allow development of sufficient physical properties.
In order to overcome such a problem, for example, Patent document 1 discloses a method wherein a silane unit including methacryloyloxy-group having high reactivity with a vinyl monomer for forming the resin component is selected and the vinyl monomer is graft-polymerized to the resultant modified polyorganosiloxane component, thereby obtaining a graft copolymer having a high graft efficiency. In order to improve graft efficiency with broad options, and without limitation to specific graft-linking agents, for example, Patent document 2 discloses a graft copolymer obtained by polymerizing a monomer composed of a polyfunctional monomer represented by allyl methacrylate as main components, and furthermore polymerizing a vinyl monomer under existence of particles of (modified) polyorganosiloxane. It also shows that since this graft copolymer has a high efficiency of grafting to polyorganosiloxane particles, more polyorganosiloxane particles can be introduced into a matrix resin even with a small amount of vinyl monomer while securing dispersibility, and therefore a resin composition obtained by blending the graft copolymer into thermoplastic resins, especially polycarbonate based resins, satisfactorily develops not only impact resistance but also flame retardancy. However, further improvement will be expected in order to fulfill higher market demand nowadays requiring development of higher flame retardancy even in shaped articles having a small thickness.
Patent Document 1: JP 60-252613 A
Patent Document 1: JP 2003-238639 A